For many years aerial tramways, such as chairlifts and gondolas, have been constructed with endless loop haul ropes that are supported and travel in a generally horizontal plane. Thus, the two sides of the endless loop are in side-by-side horizontal relation as they travel between the aerial tramway end terminals or stations. The passenger carrier units are permanently or detachably affixed to the haul rope for movement back and forth between the end terminals on the two sides of the single haul rope.
More recently, aerial tramways have been constructed in which the endless haul rope is oriented in a generally vertical plane. Thus, an upper haul rope portion is superimposed over and is generally aligned with a lower haul rope portion, with the upper and lower haul rope portions traveling in opposite directions between the tramway end terminals in a generally vertical plane. Intermediate towers are provided for support of the haul ropes in spaced apart, vertically aligned relation.
Typical of such an aerial tramway system is the aerial tramway disclosed in French Pat. No. 2,448,464 to Creissels. In the Creissels patent, the vertical orientation of the haul rope is employed to provide additional support for heavy carrier unit loads. This is accomplished by attaching a carrier unit grip assembly to the lower haul rope portion and providing a carriage or trolley on which pulleys or sheaves are provided that rides the upper portion of the haul rope. Since the upper haul rope portion is traveling in a direction opposite to the lower haul rope portion on which the grip assembly is coupled, the sheaves riding the upper haul rope are rotating at a velocity which is twice the velocity of advancement of the carrier unit. In the Creissels patent, the haul rope is operated at a lower speed when heavy loads are conveyed so that the angular velocity of the auxiliary support sheaves on the top portion of the haul rope does not become excessive.
The Creissels tramway system also includes pairs of side-by-side, vertically oriented, endless loop haul ropes with a gripping mechanism that is attached to the lower haul rope portions of both of the side-by-side haul ropes. Moreover, the carriage sheaves which support the carrier unit load on both of the upper haul rope portions. The two side-by-side haul ropes are driven in synchronism by mounting the vertical drive bullwheels to a common axle. In such a system the weight of the carrier unit is supported by no less than four cable strands. This is particularly advantageous since the size and payload weight of aerial tramway passenger carrier units has dramatically increased in recent years.
The aerial tramway disclosed in the Creissels patent, however, does not address two very important problems which occur when conveying passenger carrier units by one or two vertically oriented, endless loop haul ropes. First, merely driving the haul ropes by bullwheels which are mounted on a common shaft will not insure synchronism of haul rope motion. Small variations in the bullwheel diameter as a result of manufacture or wear, as well as differences in the traction and tensioning forces on the haul ropes, will cause the haul ropes gradually to be driven out of synchronism. This results in skewing of the passenger carrier unit between the haul ropes. My pending patent application Serial No. 07/031,927 entitled "Aerial Tramway System And Method Having Parallel Haul Ropes And Vertical Bullwheels" discloses a system in which the diameter of the bullwheels can be dynamically varied during operation to maintain synchronism of the advance of the haul ropes, thus solving this problem.
A second problem, which has not been truly resolved in connection with the Creissels tramway system, is the passage of the passenger carrier units over intermediate towers and into and out of the end terminals or tramway stations. This problem is particularly acute if the tower assembly is a counterweight tower assembly or other haul rope tensioning system. The Creissels patent in FIG. 2 shows the passage of the passenger carrier unit over a gantry tower and in FIG. 4 shows the passenger carrier unit approaching a counterweight tower assembly. In the Creissels FIG. 2 showing, however, the carriage sheaves (rolling elements 48 and 46) which engage the upper haul rope portion have been eliminated and what appears to be a grip is shown as the unit passes over upper tower sheaves 66. Since the upper and lower haul ropes are moving in opposite directions, it is obvious that the upper and lower portions of the Creissels haul rope cannot both be gripped. If sheaves 46 and 48 are to be used, they must be able to pass beyond the intermediate support towers. Such a system would require sheave-to-sheave contact at the support towers, or some modification of the support towers not disclosed in the Creissels patent.
The problem is more difficult if the intermediate tower carries a counterweight assembly or other haul rope tensioning device (e.g., pneumatic or hydraulic tensioning apparatus). Such counterweight or tensioning assemblies are more complex and conventionally require passage of the rope out of its normal path, e.g., down beneath a free floating, weight-carrying or pneumatically displaced pulley or sheave. It is apparent from FIG. 4 in Creissels that the grip of the passenger carrier unit cannot proceed past the counterweight assembly.
As is also apparent from Creissels, the passenger or cargo carry units cannot pass beyond the Creissels' bullwheels. Accordingly, Creissels positions the counterweight assembly proximate the vertical drive bullwheel, with the passenger carrier units being detached from the haul rope prior to reaching the counterweight assembly and prior to reaching the bullwheels. This solution to the problem obviously limits the location of the counterweight assembly along the tramway to positions immediately proximate the end terminals and makes the end terminals more complex and costly to construct.
Accordingly, it is object of the present invention to provide an aerial tramway assembly and method in which the advantages of support of a carrier unit from the upper and lower portions of a vertically oriented haul rope can be realized while providing a structure and method which will enable the passenger or cargo carrier unit to be conveyed easily through intermediate support towers, including counterweight or cable tensioning support towers.
Another object of the present invention is to provide an aerial tramway system in which both the upper and lower portions of a vertically oriented, endless loop haul rope can be used to support the carrier unit weight along lengths of the tramway course in which auxiliary support of the carrier unit weight is most required.
Another object of the present invention is to provide a method for supporting a passenger or cargo carrier unit from an aerial tramway haul rope which is vertically oriented that facilitates the location of haul rope tensioning tower assemblies anywhere along the tramway course.
Still a further object of the present invention is to provide a carrier unit for an aerial tramway which can be conveyed through intermediate haul rope support towers having conventional haul rope support sheave assemblies.
Another object of the present invention is to provide an aerial tramway system and method which is suitable for use in tramways having vertically oriented, endless loop haul ropes in order to support relatively heavy passenger or cargo carrier units which is relatively economical to construct, is durable and requires minimum maintenance.
The aerial tramway and method of the present invention have other objects and features of advantage which will become more apparent from and are set forth in the accompanying drawing and following description of the Best Mode Of Carrying Out The Invention.